An integrated circuit (IC) device provides various electrical, signal processing, or data processing functions by integrating multiple electronic circuits onto a package, or die, based upon the design requirements of the IC device. For example, an IC device can perform digital logic operations, analog signal operations, or mixed signal (i.e., digital and analog) operations on a single IC device. In order to save power on an IC device, the operating voltages are typically selected at a minimum voltage level needed to ensure proper operation of the circuits of the IC device. As a result, the signal levels in an IC device are typically low, e.g., no larger than necessary, and therefore the IC device may be susceptible to various electromagnetic interference modes that can inject energy into the IC device, which can cause signals to have spurious signal levels on the IC device. The existence of spurious signals may result in faulty operation of the IC device. In particular, analog IC devices and mixed signal IC devices may be particularly susceptible to the ill effects of electromagnetic interference.
Electromagnetic interference can appear in an IC device as unwanted noise on the power rails of the IC device. Noise on a power rail of an IC device is particularly pernicious because a power rail is typically shared by multiple circuits of the IC device. A designer of an IC device can attempt to design each circuit on an IC device to be immune to the effects of power line noise, for example by designing a circuit with an improved power supply rejection ration (PSRR) by improving the ability of the circuit to maintain an output level in response to a noisy power rail. However, improvements to a circuit's PSRR are typically limited to a narrow operating bandwidth of the circuit and the IC device may remain susceptible to noise outside of this bandwidth, e.g., high frequency noise on the power rails. Moreover, following the approach of designing for improved circuit PSRRs, multiple circuits may need to be redesigned in order to mitigate the effects of noise on a particular power rail.
Another approach to reducing noise on the power rails of an IC device is to provide the power rails by one or more voltage regulators, either on the IC device itself, or external to the IC device. For example, a particular circuit of an IC device may be known to be particularly noisy, that is, that the circuit is known to be a source of noise injected onto the power rail for the circuit. Here, the designer can provide one voltage regulator for the noisy circuit, and can provide another voltage regulator for other circuits of the IC device, thereby isolating the other circuits from the ill effects of the noisy circuit. Further, by designing a voltage regulator between a noisy power source and the circuits of an IC device, the voltage regulator can function to isolate the circuits from the noisy power source. Also, by including multiple voltage regulators to an IC device at different voltage levels, the power supplied to the circuits of the IC device can be supplied at more optimal voltage levels based upon the characteristics of the particular circuits. However, the use of voltage regulators may not completely eliminate noise on the power rails of an IC device.
The use of the same reference symbols in different drawings indicates similar or identical items.